Let's get some things straight... Picture

As a matter of fact, Slenderman has been around on the internet for a good three years before the game was created. The game just made him mainstream. I'm surprised by how many people don't know this.

Edit: FAQ-READ BEFORE YOU COMMENT

"Where did Slenderman come from then?"A: On June 8th, 2009, a “’paranormal pictures” photoshop contest was launched on the Something Awful (SA) Forums.The contest required participants to turn ordinary photographs into creepy-looking images through digital manipulation and then pass them on as authentic photographs on a number of paranormal forums. Something Awful users soon began sharing their faux-paranormal creations with layered images of ghosts and other anomalies, usually accompanied by a fabricated witness account to make them more convincing. On June 10th, SA user Victor Surge posted two black and white photographs of unnamed children with a short description of “Slender Man” as a mysterious creature who stalked children. The urban legend has inspired fan arts, fictional creepypastas and a mockumentary series in the style of the 1999 indie horror film Blair Witch Project. (Snipped from Know Your Meme).

"Wasn't he based off European mythology?"A: No, he wasn't.

"But there have been many old legends about a creature similar to Slenderman! Seriously, I've done research! Didn't you hear about Grobmann, Treeman, etc.???"A: None of those names and "old legends" were around prior to his creation. They were all made up by Slenderman's creators and Creepypasta writers to add "spice" to his backstory. There is no such thing as a "Grobmann" in German mythology. And there are definitely no tall, tentacled creatures in any Egyptian legend.

"But there are ancient woodcuts and paintings about Slenderman!"A: Those woodcuts and paintings are fake. They are famous woodcuts and paintings that have been heavily photoshopped to make the figures resemble Slenderman. It doesn't take an art historian to know this, people! (For more info, click here: [link])

"Slenderman wasn't created on the internet! There have been real sightings of him! Seriously, I saw him with my own eyes!"A: Really? That's cool! Ever heard of Mothman? I've seen him many times, he's a pretty cool guy. Ever heard of Kuchisake-onna? I've seen her many times too-she's actually my godmother.